At about 29 per cent slimmer (55mm vs. 77mm in width; the differences in height and thickness are negligible) and 38 per cent lighter (155g vs. 250g) than the latter, it's bound to attract those who deem the 10,400mAh version expensive (really!?), too bulky to carry around, or those who don't need to recharge their devices multiple times over.

We shan't go into great length for this review, since most of what we've written for the 10,400mAh version also applies to this 5,200mAh version.

In a nutshell, it has the same CNC-machined and anodized aluminium shell, the same button and input/output ports (albeit arranged slightly differently due to the smaller casing), and the same reliability and environmental testing results.

The battery cells are again sourced from either LG or Samsung (just that it uses two cells instead of four) and the USB smart-control and power management chips come from Texas Instruments, so it has the same voltage, current, and temperature protection mechanisms just like the 10,400mAh Mi Power Bank.

So far, so good.

2 important differences

1) Conversion rate

The first difference that caught our attention between the 5,200mAh and 10,400mAh Mi Power Banks is the former has a lower maximum conversion rate - more specifically, 85 per cent vs. 93 per cent.

Broadly speaking, this means that while the 5,200mAh version has half the capacity of the 10,400mAh power bank, the number of recharges you get from the former isn't exactly halved of what you'd get from the latter.

The numbers given by Xiaomi illustrate this clearly. For example, the 10,400mAh power bank is able to recharge the Mi 3 smartphone or iPhone 5S smartphone 2.5x or 4.5x respectively, but the 5,200mAh power bank is rated at 1x or 2x respectively.

Figure for charging the iPad Mini tablet is omitted for the 5,200mAh power bank not because it doesn't work on tablets (more on that later); more likely, it's because it doesn't have enough juice to recharge the tablet fully.

For nerds interested in conversion rate, know that the 18650-type battery used by both Xiaomi power banks has an output voltage of 3.6V. This needs to be boosted to about 5V internally in order to supply the correct output for the smartphone or tablet.

The conversion/boosting/current-switching process inevitably results in drops in efficiency.

In reality, the overall (true?) conversion rate of power banks using 18650 batteries (i.e., one has to consider the efficiency of both the power management IC and the batteries used, among others) is usually around 60 to 65 per cent, which looks to be the case for the 5,200mAh Mi Power Bank.

The 10,400mAh seems to fare better; we estimated it to be around 70 to 75 per cent.